As shown in FIG. 1, a Long Term Evolution (LTE) system architecture in the related art comprises: a Mobility Management Entity (MME), a Serving GateWay (SGW) and Evolved Node Bs (eNBs); wherein, an interface between user equipment (UE) and the eNB is a UU interface, an interface between the eNB and the MME is an S1-MME (S1 for the control plane) interface, an interface between the eNB and the SGW is an S1-U interface, and an interface between the eNBs is an X2-U (X2-User plane) or X2-C (X2-Control plane) interface. In LTE, the protocol stack of the S1-MME interface is divided from bottom to up into the following protocol layers: L1 protocol, L2 protocol, Internet Protocol (IP), Stream Control Transmission Protocol (SCTP), S1-Application Protocol (S1-AP). In LTE, the protocol stack of the S1-U interface is divided from bottom to top into the following protocol layers: L1 Protocol, L2 protocol, User Datagram Protocol/Internet Protocol (UDP/IP), GPRS Tunneling Protocol-User plane (GTP-U).
Currently, due to the lack of spectrum resources and the sharp increase of high-traffic services of mobile users, in order to increase the user throughput and enhance the mobility performance, the demand of using a high-frequency point (such as 3.5 GHz) to perform hotspot coverage is increasingly obvious, and using low-power nodes becomes a new application scenario. However, since the signal attenuation at a high-frequency point is relatively serious, the coverage of the new cells is relatively small, and the new cells do not share stations with the existing cells, therefore, if a user moves between these new cells, or moves between the new cells and the existing cells, frequent handover processes are inevitably caused, consequently the user information is frequently transferred between the evolved node Bs, which causes a great signaling impact on the core network, and further restraints the introduction of a large number of small cellular evolved node Bs at the wireless side. As shown in FIG. 2, under small cell deployment architecture, the dual connectivity service of the user plane can reduce the frequent handovers due to the movement of the user equipment. The dual connectivity of the user plane means: user data may be distributed from the core network via the Master eNB (MeNB) to the user, or from the core network via the Secondary evolved node B (SeNB) to the user. Wherein, an interface between the user equipment and the evolved node B is a UU interface, an interface between the MeNB and the MME is an S1-MME interface, an interface between the MeNB, the SeNB and the SGW is an S1-U interface, and an interface between the eNBs is an Xn interface. After the user accesses to the MeNB, the dual connectivity may be implemented by the way of adding, modifying or deleting the SeNB.
On the other hand, along with a wide range of user demands for local services and INTERNET services, for the user equipment (UE) and the core network, a permanent online function needs to be supported (i.e., after a data connectivity is established, the UE may send data to an external data network at any time, while the external data network may also send data to the UE). The external data network refers to an IP network that does not belong to the Public Land Mobile Network (PLMN), but has a connection with the PLMN. For the LIPA@LN (Local IP Access at Local Network) or SIPTO@LN (Selected IP Traffic Offload at Local Network) function, if the gateway supporting the LIPA or SIPTO service is separated from the evolved node B (which may be a macro evolved node B or a home evolved node B), we call the gateway as a standalone GW, and the standalone gateway usually also supports the SGW function. FIG. 3 is a schematic diagram of the architecture of an SIPTO@LN standalone LGW, and under the architecture of the SIPTO@LN standalone LGW, the SGW and the PGW (commonly referred to as LGW) of the UE are located in the wireless-side access network, and are separated from the (H)eNB.
In the relevant LTE system, in order to implement the SIPTO@LN function, under the scenario of a standalone gateway, the concept of local home network is defined, that is, a set of evolved node Bs or home evolved node Bs achieve local IP access to SIPTO@LN via one or more standalone gateways. The LHN ID (Local Home Network ID) is used to uniquely identify the local network in one PLMN. Currently one gateway can only belong to one LHN ID. The evolved node B (which may be a macro evolved node B or a home evolved node B) needs to report the locally supported LHN ID to a core network through a UE-specific message, and the SIPTO service PDN GW (Packet Data Network Gateway) selection is performed by selecting a service standalone gateway according to the LHN ID provided by the evolved node B or the home evolved node B ((H)eNB). Therefore, the (H)eNB needs to carry the LHN ID in an INITIAL UE MESSAGE and an UPLINK NAS TRANSPORT message.